The present invention relates to a magnetic bubble memory device (or bubble device) and a method for operating the same. More particularly, it relates to a replicate gate and a method for operating the same.
In recent years, work has progressed toward the realization of a high density storage magnetic bubble memory device in which the bit period is 4 .mu.m or less, and the memory capacity is 4 Mbits or more. A number of approaches have been proposed to such a high density storage bubble device. A very promising proposal is a bubble device which comprises a magnetic layer having: a first region having an easy axis of magnetization extending in a certain direction; and a second region surrounding the first region and having an easy axis of magnetization substantially perpendicular to that of the first region, the first region defining a plurality of bubble propagation patterns. The propagation patterns (i.e., the first region) of the above-mentioned kind of bubble device may be made by various methods, among which an ion-implantation technique is the most common. In accordance with this technique, ions, such as H, Ne, or He, are implanted into the regions other than the above-mentioned first region (i.e., the propagation patterns) of a magnetic layer having uniaxial anisotropy with the easy axis of magnetization perpendicular to the surface thereof, so as to define the above-mentioned second region. Such a bubble device, in which the propagation patterns are made by using an ion-implantation technique, is usually called an "ion-implanted bubble device".
On the other hand, in bubble memory devices, the replication of bubbles is an important function for realizing non-volatility of stored information. Particularly, in a major-minor loop-organized bubble device, a block replicate system is generally used in which a plurality of replicate gates are disposed between the major line and the respective minor loops and interconnected in series so as to form a block replicate gate by which the information bubbles in the minor loops are replicated, in the block, onto the major line. The block replicate system can provide advantageous features, such as a short cycle time and simple control for information integrity.
However, with the above-described ion-implanted bubble device, it is impossible to use the block replicate system such as used in conventional permalloy bubble devices. That is, the replication of bubbles is accomplished by stretching the bubble and then cutting the stretched domain. In a conventional permalloy bubble device, the bubble can be passively stretched by a permalloy element. However, no method has been found for passively stretching the bubble for an ion-implanted bubble device. Accordingly, the bubble must be actively stretched. Therefore, it is necessary to design a new replicate gate for the ion-implanted bubble device.
There have been proposed some replicate gates which are adapted for use in an ion-implanted bubble device. However, the proposed replicate gates are disadvantageous in that the operating characteristics are insufficient and the construction and the manufacturing process are complicated, as will be described hereinafter with reference to the drawings. In particular, it is difficult to provide a block replicate gate able to be disposed in the small area defined between the major line and the minor loops. These disadvantages make it difficult to realize a 4 .mu.m or less period bubble device whose chip architecture is compatible to that of the present permalloy bubble device.